The proposed research aims to develop a brain-computer interface that uses chronically-implanted cortical electrodes in the monkey to control stimulation of arm muscles. Monkeys will be trained to match wrist torque targets, and cortical neurons will be identified that are modulated during wrist movements. Subsequently, we will test that these cortical units can be volitionally controlled by the monkey using an operant conditioning paradigm. After temporarily blocking peripheral nerve activity, we will connect the activity of these cortical neurons to control muscle stimulation, and allow animals to learn to produce wrist movements using this artificial circuit. In subsequent experiments, we will develop a small neurochip system that can be attached to the monkey and permit online discrimination of motor cortex activity and convert this activity into stimulation of wrist flexor and extensor muscles. This neurochip system will be completely autonomous, and represents a major step toward permitting artificial stimulating circuits to function during free behavior. The long-term goal of the proposed research is to develop an implantable brain-computer interface capable of bypassing spinal cord lesions and restoring movement to spinal cord injured patients.